Exposure to heterocyclic amines (HA) derived from cooked food has been implicated as an important dietary risk factor in the etiology of certain human cancers. 2-Amino-1-methyl-6- phenylimidazo[4,5-b]pyridine (PhIP) is the most mass abundant HA found in cooked beef and chicken and has been shown to be carcinogenic in rodents in various tissues. Past studies have indicated that the genotoxicity of PhIP differs from that of other Has such as 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline (MeIQx) or 2-amino-3-methylimidazo[4,5-f]quinoline(IQ). The mechanisms involved in this differential toxicity have yet to be fully defined but appear to be related to metabolism. The bioactivation of PhIP, as well as other HAs is highly dependent upon the cytochrome P450-mediated Nhydroxylation of the parent amine to the corresponding N-hydroxy intermediate. This is followed by esterification by sulfotransferase and/or acetyltransferase, which form highly reactive compounds that can bind DNA. Studies have shown that in humans glucuronidation of N-hydroxy-PhIP is a major conjugation reaction, which leads to unreactive N-hydroxy-PhIP-glucuronides. Thus, susceptibility to the genotoxic effects of heterocyclic amines, specifically PhIP, may be influenced by metabolic activation/detoxification processes and causally related to both cytochrome P450 activity and to the levels of enzymes involved in conjugation reactions. The purpose of these studies is to understand the mechanisms involved in PhIP conjugation reactions, specifically glucuronidation, and to understand how different levels of enzyme expression affect the bioactivation/detoxification of PhIP. This should provide for a better understanding of individual susceptibility to the carcinogenic risks from PhIP exposure. The proposed studies will address the following questions: 1) What is the role of glucuronidation in the bioactivation/detoxification of PhIP and other heterocyclic amines?; 2) Do differences in PhIP metabolite levels in humans correlate with differences in specific enzyme expression, and can these differences predict inter-individual variation in PhIP bioactivation/detoxification?; 3) Is the HA imidazofuropyridine (IFP) similar to PhIP with regards to metabolism and genotoxicity, and what is IFPs contribution to the overall risks associated with heterocyclic amine exposure?